1. Field of the Invention
The invention relates generally to a method of making magnetic powders for use in the manufacture of magnetic recording media. More particularly, the invention relates to an improvement in the borohydride process of making magnetic powders of the indicated type.
2. Description of the Prior Art
It is known to make magnetic powders of the indicated type by the borohydride reduction of salts of ferromagnetic elements. Examples of such methods are those described in U.S. Pat. Nos. 3,932,293; 4,009,111; and 4,096,316.
Although the aforecited patents disclose various processes for producing magnetic powders, no one of said patents teaches that the coercive force (H.sub.c) of the resulting powder can be controlled by the utilization of critical temperature conditions. Accordingly, there has been a need for a workable method of making magnetic powders of the indicated type having a selected and predictably controlled coercive force. In the manufacture of magnetic recording media it is critical that the coercive force of the media be controlled to a predetermined magnitude. It is important that such media have a predetermined coercivity so that they can function in a predictable manner as tapes, discs or the like. Moreover, this desired coercivity varies with a particular application.
Other prior art methods known to applicant are those disclosed in U.S. Pat. Nos. 4,101,311; 4,076,861; 4,069,073; 4,063,000; 3,966,510; 3,756,866; 3,661,556; 3,567,525; 3,535,104 and 3,206,338.
As discussed above, none of these patents teaches that the coercive force of the magnetic powder produced by the borohydride process can be controlled to a predictable magnitude.